Organisms that feed on dead organic matter, returning the broken down matter (eg. minerals) back to the soil and air, making it available to other living organisms in the ecosystem.
Define trophic level (SPEC).
The level at which an organism feeds in a food chain.
__ __ and __ __ show how energy is __ through an ecosystem. What are the differences in what these two show? Energy locked up in the things that can't be eaten (eg. __ and __) are recycled back into ezosystem by ___.
Food chains show simple lines of energy transfer.
Food webs show many different food chains, showing how energy flows through the whole ecosystem.
bones and faeces
Why are there less living tissue at higher levels of the food chain? Give different ways of how energy is lost.
Because at each trophic level, some energy is lost from the food chain, and therefore unavailable to the organism at next trophic level.
Eg. Respiration releases energy from organic molecules like glucose, and some are converted to heat.
Eg2. Energy remains stored in dead organisms and waste material (available to decomposers instead).
Eg3. Impossible for consumers to make full use of plan't biomass - some plants die and consumers don't eat every part of plant, and they don't digest everything they eat.
List 3 ways of measuring efficiency of energy transfers between each trophic level.
Pyramids of biomass - measure dry mass
Pyramids of energy - burn organisms in a calorimeter to work out how much energy is released per gram of biomass.
Productivity - look at rate at which energy passes through each trophic level in food chain.
Discuss these different ways of measuring efficiency of between trophic levels.
Biomass: Ad: number of organisms doesn't provide accurate pic of how much living tissue there is at each trophic level, so biomass is better. Disad: Hard to measure dry mass - as this would mean heating organisms up to 80oC. Also, doesn't take in the fact that different species may release different amounts of energy per unit mass.
Energy: Ad: can measure energy per unit mass. Disad: involves burning organisms (so destructive to environment etc..). Also isn't accurate representation of energy transfer, to show the energy of two trophic levels (one trophic level could be taking energy from other organisms too.)
Productivity: Measures in kilojoules of energy per square metre per year - available to different organisms. Gross primary productivity (GPP) is rate at which plants convert light energy into chemical energy. Net primary productivity (NPP) is the energy left after the energy supplied plant's own needs (eg respiration) available to next trophic level.
The energy captured by leaves for photosynthesis is called the ___ ___. Some of this will be used by plant and lost as __ ___. Difference between these is the __ ___ __.
net primary productivity (NPP)
[may be measured in terms of energy per unit time]
Explain ways in which human activities can improve net primary productivity. (7)
Some crops planted early to provide longer season to harvest more light. Others are grown under light banks - increase rate of photosynthesis and hence NPP.
Drought-resistant strains bred
Greenhouses provide warmer temp, also again earlier growing season.
Crop-rotation and including nitrogen-fixing crops like peas or beans. Also fertilizers for minerals.
Pesticides, fungicides and herbicides
Some plants have been bred to be pest-resistant, to be resistant to fungal infections.
Some plants genetically modified to be pest-resistant or resistant to fungal infections.
So, whole point in increasing productivity is so that organisms can put the highest possible amount of energy into increasing biomass so that it is available, eventually, to humans. How can humans increase secondary productivity by manipulating energy transfer from producer to consumer? (3)
Selective breeding to produce breeds with faster growth rates, increased egg production and milk production etc.
Animals treated with antibiotics to avoid unnecessary loss of energy to pathogens and parasites.
Mammals and birds waste a lot of energy walking around to find food and keeping their temp warm. By keeping animals in controlled conditions (eg indoors) with fixed temp and stopping animals from moving about and providing food means more energy allocated to meat production.
Some people become vegetarians to stop rainforests being cut. Explain their reasoning.
A lot of land is cleared to make space to grow animals. The land could instead be allocated to arable crop production.
Because arable crop production involves shorter food chains (wheat---humans), less energy is wasted rather than in longer food chains producing farm animals (grass---cows---humans).
So, if fewer people eat meat, more land would be used for arable crop production, and less rainforest would need to be felled.
What is succession?
Directional change in a community of organisms over time.
Because a community of organisms can cause a change in habitat, and change in habitat causes change in make-up of community.
1) What is primary succession? 2) What is a climax community?
1) A directional change in a community of organisms over time, beginning from bare ground.
2) The final stage at the end of the process of succession, where a stable community is reached.
[Remember that succession does not always start from bare ground (no soil), secondary succession takes place on previously colonised habitat.]
Describe one example of primary succession resulting in a climax community.
Succession on sand dunes:
1. Pioneer plants/community like sea rocket clonise the sand just above the high water mark. These can tolerate salt water spray, lack of fresh water and unstable sand.
2. Wind-blown sand builds up around base of these plants, forming 'mini' sand dune. As plants die and decay, nutrients accumulate in this mini dune. As dune gets bigger, plants like sea couch grass colonise it. Because sea couch grass has underground stems, it helps stabilise the sand.
3. With more stability and accumulation of more nutrients, plants like marram grass start to grow - this is special, as they grow taller to stay above growing dune, trapping more sand (as their shoots trap wind-blown sand).
4. As sand dune and nutrients build up, other plants colonise the sand. Plants of the members of the bean family (legumes) start to grow and fix nitrate ions in dune. With this nitrate ions available, more spies colonise the dune, and this stabilises the dune to a climax community. (might be a woodland - CHECK)
Give another example (maybe easier, so learn this one maybe) of primary succession resulting in climax community.
1. Algae and lichens begin to live on the bare rock - the pioneer community.
2. Erosion of rock, and build-up of dead and rotting organisms produces enough soil for larger plants like mosses and ferns to grow. These replace, or succeed, the algae and lichens.
3. IN similar way, larger plants succeed these small plants, until a final, stable community is reached when the soil is deep enough and rich enough in nutrients. This is called a climax community. In UK, climax communities are often woodland communities.
Investigating populations of organisms involves looking at the ___ and ___ of species in a particular area. Describe what each is.
Abundance: number of individuals of one species in a particular area.
Distribution: presence or absence of particular species in particular areas.
Because it's time-consuming to measure all the individuals, you take a __ of the area you're investigating. How do you choose a random sample? And then what calculation do you need to do to estimate the number of individuals in the whole area?
Could pick random sample sites by dividing the field into a grid and using a random number generator to selevt co-ordinates.
Use appropriate technique to take sample (eg. quadrat or transect) and repeat.
Number of individuals for whole area can be estimated by taking an average of data collected from each sample and then multiplying it by size of the whole area. (Percentage area can just be found by the average of all the samples).
How do you work out what how many quadrats should be used for a specific area, what needs to be done?
A pilot study
Take random samples from across habitat and make cumulative frequency table.
The quadrat number that gives the point where the cumulative number starts to stay the same is the number of the quadrats required.
Describe how you would use a quadrat (frame quadrat) to measure distribution and abundance of organisms.
Square frame divided into a grid of 100 smaller squares by strings attached across the frame.
Place this on a random point and you can either...
Check the presence or absence of a species (for distribution)
Or count how many individuals there are in each quadrat. Sometimes, like for grass and moss, it is very hard to count individuals, and in this case, use measure percentage cover of the species.
Describe how you would use a point quadrat to measure abundance of organisms.
The pins are dropped through the holes in the frame and every plant that each pin touches is recorded. Then count the number of individuals.
Percentage cover can be measured by calculating the number of times a pin has touched a species as a percentage of the total number of pins dropped.
Transects are useful for studying what in a habitat especially? Describe the two types of transects you can take.
Useful for measuring changes in vegetation across a habitat. A line transect is a line taken across a habitat.
Line transect: at regular intervals, make a not of which species is touching the tape. (might not have to be at regular intervals - that might be interrupted line transect)
Belt transect: at regular intervals, place a quadrat next to the line (interrupted belt transect) studying each. Alternatively, place qudrat next to line, moving it along line after looking at each quadrat. (Continuous belt transect).
[Remember, the belt transect is advantageous over line in that it provides abundance info as well, whereas line transect only really measures absence/presence. However, it is a lot more work.]